Transfer value from a input text.

Transfer value from a input text.

Hello to everybody,
I need help to transfer a value from an input text to javascript function.

This is my hidden input text:
<input name='VarJs' type='hidden' size='10' id=VarJs' value='<?php $Id ?>'  />

I'd like to transfer this value from php to js and then I'd would like to use it in another js function.

Thanks in advance.

Tegatti